The present invention generally relates to apparatus for providing a reference laser beam and, more particularly to a polygonal lighthouse assembly for use in such apparatus, the lighthouse assembly having transparent panes assembled together in an arrangement which provides an improved corner configuration.
Laser beam systems have been employed in numerous surveying and construction applications. In one such system disclosed in U.S. Pat. No. 4,062,634, which issued Dec. 13, 1977 to Rando et al and is assigned to the assignee of the present invention, a laser beam projecting apparatus provides a rotating laser beam which establishes a reference plane. Typically, the rotating laser beam is used to provide a continuous, visible plane of light that creates a constant horizontal benchmark of elevation over an entire work area. Also, the system employs one or more laser beam detectors placed at considerable distances from the projecting apparatus for intercepting the rotating laser beam and determining elevation at selected points throughout the work area.
In the laser beam projecting apparatus, the generally horizontal rotating reference laser beam is produced by projecting the beam generally upward and then deflecting it ninety degrees within a pentaprism or penta-mirror assembly. The pentaprism assembly is rotated about a vertical axis within the projecting apparatus to cause the horizontal beam to rotate and define the horizontal plane.
In another type of laser beam projecting apparatus, a stationary plane of reference laser light is produced by projecting the beam generally upward and then deflecting the beam laterally by means of an inverted conical reflector. The conical reflector is aligned with its apex in the center of the beam and its axis aligned with the beam. To adapt either type of reference laser beam projecting apparatus for use in surveying and construction applications under a variety of field conditions, the projecting apparatus is provided with a waterproof housing having an upper transparent lighthouse assembly within which the pentaprism assembly rotates or the conical reflector is positioned and through which the laser beam is projected. The lighthouse assembly typically includes four upstanding flat transparent panes of glass of high optical quality which are joined together to form a polygonal structure with generally vertical corner junctures at their side edge portion surfaces. Four posts are threadably mounted between a top casting of the housing above the panes and upper rim of the housing below the panes for applying sufficient axial forces to pull them together and lock the panes into appropriate seats. The four posts are aligned radially outwardly of the generally vertical corner junctures formed between the panes, while the panes have forty-five degree bevel side edge surfaces which interface to form the corner junctures and are sealably mounted together by a suitable adhesive.
For the most part, the overall performance of the above-described types of reference laser beam projecting apparatus has met and even surpassed expectations. However, difficulties have been experienced with regard to the ability to construct and assemble lighthouse pane corner junctures to the standard of precision necessary and desired to reliably avoid degradation of beam continuity as it passes through the corner junctures.
It is, therefore, seen that a need exists for an improved lighthouse assembly construction which will eliminate difficulties encountered at the corner junctures of the panes in prior art lighthouse assembly constructions.